You have probably already checked this but doesn't hurt to ask: The "group_address@outlook.com" you are referring to works just fine outside of the Rails app, correct? Sounds like an outlook or group issue with that email address, don't see why Rails would care if the email represents a group of emails or an individual email address.
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tronmcpJun 26 '13 at 23:44

yeah, I checked it and it's actively being used.
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cluvJun 27 '13 at 15:26